Why does security light stay on and runs down battery?

THE SECURITY SYSTEM IS SHUTTING THE CAR DOWN. IT IS YOUR OVERALL PROBLEM

Two things will cause this, both are shorts in computers. One is the body control module, which stores the security system. The other would be the instrument panel. My guess would be the IP. usually when it happens with the BCM, the vehicle won't start. As long as it doesn't drain the battery, I wouldn't worry about it.

It will run until you run the battery down,take it to autozone they will check your alternator for free.

Alternator will keep engine running when battery becomes disconnected through a loose or corroded connection.

It sounds like an alternator, yet you say the fan still worked after you disconnected the battery? And the car was still running? Or the car died out. Sorry, need some more details on this one.

The way I used to check alternator is while car is running I would take the negative cable off the battery if the car dies then the alternator is not putting out enough. The battery is used to crank the car. When the car is running the alternator provides voltage to run the car and charge the battery back up. Now day some car have some security which if the car dies when you take the cable off the anti theft will not let radio work till you put a code in it.
If not your battery or alternator it may be something draining your battery while it is off. If you have a light in the trunk, under hood under dash which may be staying on. I had a portable spot light which had a charger wired into my truck. I found the battery was bad in the light and the charger was charging 24 /7 and running my battery down.

The 2000 Fords should allow the radio to continue to play until you open the driver's door. The lights may stay on for 1 or 2 minutes after you leave the car (close the driver's door) depending on the lighting/security feature of your vehicle.

Your battery should be strong enough to allow these items to remain on for several minutes. If the battery weakens that quickly, you need a new battery or you need to have your charging system inspected.

security light. should not run down a battery. check state of health on battery and see if something else is staying on. trunk light or other accessori.

One of the door pin switches is faulty, Interior light must be staying on and draining the battery. If you don't see the dome light staying on possibly the trunk switch is bad.

when key on and engine off, does the security light flash constantly? if so its shutting down the fuel pump, it starts momentarily due to the computer priming the engine with fuel. how to reset, turn key to run position, leave it on touch nothing, takes 10-12 minutes, start watching light around 10 minutes. it will stop flashing... turn key off, then back on and start this will reset the security system. they are sensitive on this platform car it will happen again. good luck!